Continuously variable transmissions operate by transferring rotational power from an input shaft to an output shaft. The rate of rotation of the output shaft, and even its direction, may be varied relative to the rate and direction of rotation of the input shaft by means of a mechanism that is presently referred to as a variator. The variator may be operated by a single control that may be moved from maximum speed in a first direction to zero output or neutral and then progressively faster speeds in a reverse direction until maximum speed position of the control causes the variator to affect maximum speed of rotation of the output shaft in the second direction.
In the usual application to a vehicle, the output shaft is operatively connected to a pair of driving elements such as wheels through a differential. Steering is generally provided by rotating a pair of non-driven wheels. In track driven vehicles it is common practice to differentially vary the rotation rates of the shafts driving each track. With propeller drives it is common practice to drive twin propellers with separate motors, using rudders for further steering control.
Continuously variable, or stepless, transmissions have been described by Andrus, U.S. Pat. No. 2,745,297; Gillade, U.S. Pat. No. 4,406,178, General, U.S. Pat. No. 3,203,277; Mills, U.S. Pat. No. 4,823,627; and Uchikawa, Japan 57-51050. Tervola in the parent, copending application Ser. No. 303,079, of which this is a continuation in part, discloses a stepless planetary gear type transmission with a variable diameter pulley/belt variator that includes a servo-mechanism for maintaining a neutral or zero output under control of a single control lever for forward, neutral and reverse. Tervola, in U.S. Pat. No. 4,718,508 teaches a steering mechanism in which a single input drives two output shafts through a pair of planetary gear systems. Each planetary gear system includes a ring gear, a sun gear and a planetary gear carrier with planetary gears that mesh with both the ring gear on the outer side and the sun gear on the inside of the circle. A power-driven shaft between the planetary gear sets has driving engagement with both of the sun gears or the planetary gear carriers and the respective output shafts are driven by the other one of the sun gears or planetary gear carriers. A steering shaft is operatively engaged with both ring gears in such manner as to hold them against rotation for straight-line propulsion with both output shafts running at the same speed. For turning, the steering shaft is rotated by a bidirectional steering motor and a steering wheel to rotate the two ring gears in opposite directions so that the two output shafts will be rotating at different speeds and may also be rotating in different directions. See also "Popular Science" July, 1985 pages 60-62 entitled "Tanks and Dozers turn on a dime with new all-gear steering". This teaches a power differential and a steering differential geared together.
It is costly to manufacture and maintain separate structures for speed control, differentials and steering according to prior art teaching that they be separate structures.